抱佛脚-刷题系列之sql

抱佛脚一时爽，一直抱佛脚一直爽！这篇文章总结常见的sql问题~
参考链接：leetcode

交换性别

---

UPDATE salary
SET
    sex = CASE sex
        WHEN 'm' THEN 'f'
        ELSE 'm'
    END;

删除重复邮箱

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DELETE p1
FROM Person p1,
    Person p2
WHERE p1.Id > p2.Id
AND p1.Email = p2.Email

比经理工资高的员工

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SELECT p1.Name AS Employee
From Employee p1
INNER JOIN Employee p2
WHERE p1.ManagerId = p2.Id 
AND p1.Salary > p2.Salary

部门最高工资

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SELECT
    D.NAME Department,
    E.NAME Employee,
    E.Salary
FROM
    Employee E,
    Department D,
    ( SELECT DepartmentId, MAX( Salary ) Salary 
     FROM Employee 
     GROUP BY DepartmentId ) M
WHERE
    E.DepartmentId = D.Id
    AND E.DepartmentId = M.DepartmentId
    AND E.Salary = M.Salary;

第二高薪水

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SELECT(
SELECT distinct salary 
FROM Employee
ORDER BY salary DESC
LIMIT 1, 1) AS SecondHighestSalary

组合两个表

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SELECT Person.FirstName AS FirstName, Person.LastName AS LastName, Address.City AS City, Address.State AS State
FROM Person LEFT JOIN Address
ON Person.PersonId = Address.PersonId

查找工资第 N 高的员工

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CREATE FUNCTION getNthHighestSalary ( N INT ) RETURNS INT BEGIN

SET N = N - 1;
RETURN ( 
    SELECT ( 
        SELECT DISTINCT Salary 
        FROM Employee 
        ORDER BY Salary DESC 
        LIMIT N, 1 
    ) 
);

END

分数排名

select a.Score as Score,
(select count(distinct b.Score) from Scores b where b.Score >= a.Score) as Rank
from Scores a
order by a.Score DESC

部门工资前三高的员工

SELECT
    d.Name AS 'Department', e1.Name AS 'Employee', e1.Salary
FROM
    Employee e1
        JOIN
    Department d ON e1.DepartmentId = d.Id
WHERE
    3 > (SELECT
            COUNT(DISTINCT e2.Salary)
        FROM
            Employee e2
        WHERE
            e2.Salary > e1.Salary
                AND e1.DepartmentId = e2.DepartmentId
        )
;